Question: Solve for $x$ : $5x^2 + 90x + 405 = 0$
Explanation: Dividing both sides by $5$ gives: $ x^2 + {18}x + {81} = 0 $ The coefficient on the $x$ term is $18$ and the constant term is $81$ , so we need to find two numbers that add up to $18$ and multiply to $81$ The number $9$ used twice satisfies both conditions: $ {9} + {9} = {18} $ $ {9} \times {9} = {81} $ So $(x + {9})^2 = 0$ $x + 9 = 0$ Thus, $x = -9$ is the solution.